A local area network system or loop distribution plant is effective to connect each telephone customer to a central office through a transmission medium. The transmission medium is commonly a twisted pair of insulated copper conductors which, for most of its length, is disposed in a multipair cable.
In a typical loop plant, a main feeder cable connects the central office to an area to be served. Branch feeder cables extend from the main cable to designated areas. Each branch cable connects to a plurality of distribution cables that extend service to a particular customer area. A distribution service cable connects a distribution cable to each customer premises.
The loop plant has evolved as new materials, methods and plant concepts were developed to provide reliable telephone service at a reasonable cost. Loop plant must be inexpensive to install and maintain, should require a relatively small amount of physical space, and be readily accessible to accommodate changes in service and in customers.
In a presently used arrangement referred to as a serving area concept (SAC), at least two copper conductor pairs are provided to each customer unit. One flexibility point, which is referred to as the serving area interface (SAI), is provided in each area and serves as an interface between cable pairs providing service from the central office and those to customer units.
In a typical SAC system for servicing residential customers, for example, a branch cable is routed from a central office main feeder cable to a serving area interface. From there, cables referred to as distribution backbone or subfeeder cables are extended across parallel streets, for example, and front or rear lot distribution laterals extended therefrom toward customers' premises. For such a system, each distribution backbone cable is tapered, that is, as it connects to each rear or front lot lateral, a portion of it is spliced to those laterals and a number of pairs from that point on are cut-dead ahead. This means that once a distribution pair is cut and spliced to a lateral pair extending toward a customer's premises, the remainder of that distribution pair to the end of the cable or ahead of the splice point is unused. As a result, half of the copper footage in these cables is wasted. Also, for each front or rear leg lateral, pairs beyond the splice points are unused. Service cables extend from the splice points to customers' premises. The splice points may include buried closures or service pedestals.
A system such as that just described has been used for some years but it does have some disadvantages. As described, it obviously includes a number of splice points each of which entails substantial labor costs, and which, historically, have been trouble points. Also, because pairs are cut-dead ahead, a portion of each cable beyond each splice point or beyond each point from which front or rear lot laterals extend goes unused.
The problems associated with presently used metallic conductor loop systems are exacerbated as the loop tends to become one in which optical fibers play a predominant role. As is known, optical fiber interface electronic devices which are required for an optical fiber loop are not yet generally available. When such devices become available, it is desirable that they be connected immediately into the loop. Accordingly, it becomes important now to provide a system which not only overcomes some of the disadvantages of prior art systems but also one which provides copper metallic as well as optical fiber capabilities to facilitate a transition from an all metallic conductor system to one in which any metallic conductors are used only to provide power.
Seemingly, the prior art does not include such a system. The sought-after system must be one which is easily installed, is economical and which includes metallic as well as optical fiber conductors.